Pakistan says its investigation into a nuclear proliferation scandal has concluded with the recent release of a close aide to A.Q. Khan. Dr. Khan led Pakistan's controversial nuclear program and is widely believed to have organized a vast nuclear black-market.

Pakistan has interrogated nearly a dozen scientists and senior officials linked to its nuclear facility since the programs lead scientist, A. Q. Khan, admitted, in 2004, he sold nuclear secrets to Iran, North Korea and Libya.

While Khan is still under house arrest, most of the other suspects were released after initial investigation but Khan's close aide, Mohammed Farooq remained under arrest for more than two years until his release last week.

Speaking to reporters Tuesday, Pakistan's foreign ministry spokeswoman, Tasneem Aslam, said that Farooq's release signals an end to the government's investigations into Khan's nuclear network. "As far as we are concerned this chapter is closed. I would presume that with Dr. Farooq's release there is a closure to that case," she said.

Officials say he was released last week but has been told to stay home for his own security.

Farooq's former supervisor, A.Q.Khan, is still widely revered in Pakistan for leading the country's nuclear program. In 2004 Pakistan President Pervez Musharraf pardoned him for selling nuclear secrets.

Khan says he acted without the government's knowledge, a claim many government critics say is difficult to believe.

The foreign ministry spokeswoman says the government will maintain its policy banning foreign governments from questioning all the scientists suspected of having played a role in the nuclear proliferation program. "We have repeatedly said that whatever information is required, questions can be forwarded to the government of Pakistan. We would get the answers. There is no question of direct access," she said.

It is widely believed that Khan played a key role in helping Iran develop its nuclear program, currently at the center of a tense international standoff.